A timewarp is an effect added to a clip to make the speed of the action taking place appear to go faster or slower than when it was originally recorded. This effect is created by increasing or decreasing the number of frames in the clip. Frames are duplicated or removed as needed and the action is interpolated over the new number of frames.
Create timewarps on the desktop, in the Batch or Player timeline, or using the Motion Blur node in Batch.